Photoelectric ice level sensor

ABSTRACT

A control circuit for a current activated thermostatic appliance control switch is presented. Current from an AC voltage source is provided through a main SCR, the gate terminal of which is connected through the emitter-base junction of an intermediate transistor to the common terminal of a low voltage rated trigger SCR and voltage dropping resistor connected in series across the AC supply. During the positive half cycle of the AC supply when the normally conducting trigger SCR is switched off in response to a predetermined external condition, current flows to the main SCR gate through the transistor emitter-base junction operating in the zener region to maintain low voltage across the trigger SCR. During negative half cycles of the AC supply the diode action of the transistor&#39;&#39;s collector base junction connected across the trigger SCR similarly maintains low voltage thereacross. The trigger SCR is shown as a light activated SCR.

United States Patent 1 [111 3,731,496 a I Frazier p 1 May 8, 1973PHOTOELECTRIC ICE LEVEL S NS Primary Examiner-James W. Lawrence [75]Inventor: Lauren L. Frazier, Louisville, Ky. Assistant Examiner-D. C.Nelms A t -W t E. [73] 9 Assignee: General Electric Company, I army 81ct Rule et a] hquisville, Y- 57 ABSTRACT [22] led: 1972 A controlcircuit for a current activated thermostatic [21] Appl 222,177 vappliance control switch is presented. Current from an AC voltage sourceis provided through a main SCR, the gate terminal of which is connectedthrough the i 307/3ll emitter-base junction of an intermediatetransistor to [51] Int. Cl. ..F25c 7/00 the common terminal of a lowvoltage rated trigger [58] Field of Search ..307/3l1, 117; SCR andvoltage dropping resistor connected in series 250/206, 209, 214, 221,222, 223; 62/137 across the AC supply. During the positive half cycle ofthe AC supply when the normally conducting trigger [56] Ref r nces CitedSCR is switched off in response to a predetermined external condition,current flows to the main SCR gate ED STATES PATENTS through thetransistor emitter-base junction operating 8 i 9 .307 m the'zener i tolow vltage across the i 13;: trigger SCR, During negative half cycles ofthe AC 3 453 450 7/1969 Evalcls: ..307 311 Supply the diode action thetransiswrs 3,660,698 5/1972 Schisselbauer ..307/311 base junctionmnnected across the trigger SCR similarly maintains low voltagethereacross. The trigger SCR is shown as a light activatedSCR.

5 Claims, 5 Drawing Figures Patented May 8, 1973 2 Sheets-Sheet 1Patented May 8, 1973 2 Sheets-Sheet 2 F-IGA- R o T C E L L o C 1PHOTOELECTRIC ICE LEVEL SENSOR BACKGROUND OF THE INVENTION The presentinvention relates to a control circuit for a current activatedthermostatic appliance control switch. It is useful in controlling theoperation of an automatic ice maker in which the level of ice pieces inthe ice storage receptacle is indicated by a light beam. In such anarrangement, when the receptacle is filled with ice pieces, the lightbeam is interrupted and this triggers the control circuit of the presentinvention to activate the thermostatic control switch which, in turn,stops the operation of the ice maker.

One control circuit useful for this purpose has been described incopending application Ser. No. 20,077 filed Mar. 16, 1970 in the name ofJohn E. Sterling. Briefly, the circuit in that application employs aphotocell to detect the light beam used to indicate the ice piece leveland a DC regulated power supply adapted to supply a low DC voltage fromthe incoming AC supply means. The photocell connected in series with aresistor across this low DC voltage forms a resistance bridge to controlthe gating of a transistor and hence the operation of an SCR, which inturn may activate a thermostatic switch, resulting in the stopping ofthe icemaking operation. Although this circuit has proved to besatisfactory for the purpose, the control circuit described inaccordance with the present invention improves over such prior artcontrol circuit by substituting a lighbactivated SCR for the photocellwith a resulting gain in reliability and sensitivity. A PNP transistoris coupled so as to take advantage of its zener and conventional diodecharacteristics to control current flow and to effect the gating of anSCR. The circuit is coupled across the household AC lines in such anarrangement of components that many of them are subjected to very lowvoltage as compared with the AC line voltage. This obviates the need fora DC regulated power supply andpermits the usage of low-level-componentswith a resultant longer life expectancy.

It is therefore an object of the present invention to provide a controlcircuit for a current activated thermostatic appliance control switchwhich is inexpensive and reliable in operation.

SUMMARY OF THE INVENTION In accordance with the present invention, acontrol circuit for a current activated thermostatic appliance controlswitch comprises means for supplying an indication of a predeterminedexternal condition intended to initiate actuation of the thermostaticswitch and means for supplying an AC voltage which includes first l andsecond input terminals. The control circuit also'includes a thermostaticheater current control SCR cou pled across the input terminals of the ACsupply means. Also included is a trigger SCR and a voltage droppingresistor connected in series across the input terminals, the trigger SCRadapted to be responsive to said external condition indication means tochange its conduction state in response to a predetermined change insaid external condition. There is further included a transistor havingits base-emitter junction connected from the anode of the trigger SCR tothe control gate of the control SCR and having its base-collectorjunction connected across the anode-cathode terminals of the triggerSCR, whereby, non-conduction of the trigger SCR causes a gating currentto flow by zener action of the transistor base-emitter junction to thegate terminal of the control SCR during positive half cycles of the ACsupply and reverse current during negative half cycles of the AC supplyis provided by diode action of the transistor collector-base junction.

BRIEF DESCRIPTION OF THE DRAWING In the accompanying drawing:

FIG. 1 is a front elevational view, partly in section, of a portion of ahousehold refrigerator including the present invention;

FIG. 2 is a vertical sectional view taken generally along line 22 ofFIG. I;

FIG. 3 is a horizontal sectional view taken generally along line 33 ofFIG. 1;

FIG. 4 is a schematic diagram of a portion of the electrical controlcircuitry for controlling the automatic operation of the ice maker; and

FIG. 5 shows symbolically the electrical equivalent of transistor 52 ofFIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENT With reference generally toFIGS. 1, 2 and 3 of the accompanying drawing, there is illustrated ahousehold refrigerator with a freezer compartment 10 having mountedtherein an automatic ice making system, the operation of which iscontrolled in accordance with the circuit of the present invention. Anaccess opening at the front of the freezer compartment is closed by adoor 12. The inner surface of the door 12 is shaped so as to form astorage recess on the interior surface.

An ice storage receptacle 13 is supported within this recess and anautomatic ice maker 14 is supported within the freezer compartment l0above the receptacle 13 in a position such that the ice pieces from theice maker 14 can be conveyed by a chute 15 to the receptacle 13.

Referring to FIG. 3, door 12 is provided with a relatively smallsecondary access opening or passage 16 extending through the door 12 atabout countertop height. This passage 16 is normally closed by asecondary or ice service door 17, the lower edge of which is hingedlysupported as indicated at 18 in FIG. 2, for tilting movement about itshinged axis.

The ice storage receptacle 13 is removably supported on the innersurface of this secondary door 17 so that when secondary door 17 istilted to its open position or when door 12 is opened, the ice stored inthe receptacle may be obtained through the open top 19 of thereceptacle. This through-the-door ice service may be of the typedisclosed in US. Pat. No. 3,602,007Drieci.

An ice maker useful in the system contemplated by the present inventionmay be of the type disclosed in 'U.S. Pat. No. 3,33l,2l5--Shaw with theexception of receptacle at a predetermined level, such as that which adesired quantity of accumulated ice pieces may reach. Also included isphoto-sensitive SCR 25 positioned on the opposite freezer compartmentframe component 23 and aligned so as to receive the beam of 5 light fromlamp 21. Components 21 and 25 are mounted at an elevation below the top19 of receptacle l3, and aligned windows, in the form of slots 28 and29, are provided in the opposing side walls of the receptacle so thatthe beam of light may traverse the receptacle to reach SCR 25 at thatpredetermined level. Similar windows 30 and 31 are provided in the innersurface of the door 12 in alignment with windows 28 and 29. The relevantportions of the ice maker circuit are shown schematically in FIG. 4 andinclude a motor 34 for driving the ice maker timing, harvesting andwater-fill mechanism, a mold heater 35 for warming the walls of the icemold to facilitate the release of the ice pieces therefrom and athermostatic switch 36 for sensing the mold temperature and initiallyenergizing the motor 34 and the mold heater 35 upon the formation of icepieces in the ice maker mold. The motor 34 drives a timing cam 37operating a plurality of switches during the ice harvesting cycle, oneofwhich energizes and opens a solenoid valve 38 for supplying a freshcharge of water to the ice maker mold after the discharge of ice piecestherefrom.

When the thermostatic switch 36 senses a predetermined below freezingmold temperature, it closes and connects both the motor 34 and the moldheater 35 to the AC supply voltage means, here illustrated as lines 39and 40. During initial operation of the motor, the cam 37 closes a firstswitch 41 bypassing the thermostatic switch 36 to assure continuousoperation of the motor and the mold heater after the mold heater 35 haswarmed the mold to a point where the thermostatic switch 36 opens.Following the discharge of ice pieces from the mold, the cam 37 closes asecond switch 42 for energization of the solenoid controlled water valve38 to supply a fresh charge of water to the mold. Further rotation ofthe cam opens both switches 41 and 42 thereby de-energizing both themotor and the mold heater which remain de-energized until the thermostatagain senses a'below freezing temperature in the mold.

in accordance with the present invention, control circuit 32,schematically illustrated in FIG. 4 of the drawing, interrupts thisautomatic ice making cycle when the ice accumulated in receptacle 13 hasreached a predetermined level. More specifically, the function ofcircuit 32 is to provide thermostatic control current to energize heater44 positioned adjacent to thermostatic switch 36 thereby causing switch36 to open preventing further operation of motor 34 and mold heater 35whenever the quantity of ice pieces in receptacle 13 reaches apredetermined level.

. In the control circuit 32 of FIG. 4, means for supplying an indicationof a predetermined external condition, such as the level of ice piecesin the receptacle 13, includes lamp 21 energized by a voltage step-downtransformer 45. Means for supplying an AC voltage includes a pair ofinput terminals and 56 connected to a 120 volt power source (not shown)via lines 39 and 40.

Current control SCR 51 has its anode connected to input terminal 55 andits cathode connected through input terminal 56 to thermostatic heater44. Resistor 62 is connected across gage terminal 61 and the cathode ofSCR 51 to prevent spurious gating of SCR 51.

A trigger SCR 25 and voltage dropping resistor 59 are coupled in seriesacross the input terminals 55, 56. SCR 25 is preferably a lightactivated SCR and is adapted to be responsive to the beam of light fromlamp 21 to be normally in the full conduction state and to change itsconduction state in response to a predetermined change in the incidentlight beam, as when the light beam is interrupted by ice pieces in afull receptacle. Bias resistor 58 is connected from the anode to theanode gate terminal of SCR 25 and determines the level of incident lightintensity at which SCR 25 conduction is changed.

Control circuit 32 further includes transistor 52 having itsbase-emitter junction connected from the anode of trigger SCR 25 to thegate terminal 61 of control SCR 51 to provide a gate current path to SCR51 during positive half cycles of the AC supply voltage when SCR 25 isnon-conducting. The collector-base junction of transistor 52 isconnected across the anode-cathode terminals of trigger SCR 25 for apurpose to be described hereinafter.

In operation, when the level of ice pieces is below the light beam fromlamp 21, the light impinges on trigger SCR 25. During the positive halfcycles of the A, voltage on terminals 55, 56, i.e., terminal 55 ispositive with respect to terminal 56, the radiant energy on SCR 25causes it to be gated into conduction in accordance with well-knownprinciples of light activated SCR operation.

In the operation of control circuit 32, during the positive half cycleof the AC supply voltage, i.e., when the voltage at terminal 55 ispositive with respect to that at terminal 56, the anode-cathodes ofcontrol SCR 51 and trigger SCR 25 are forward biased. Assuming theaccumulation of ice pieces in receptacle 13 is below the light pathbetween lamp 21 and SCR 25, when the anode-cathode bias of SCR 25 issufficiently positive, the beam of radiant energy impinging upon SCR 25will cause it to switch to the conduction state with a voltage dropthereacross of approximately 1 volt. Since the voltage level at point 63is below the 6 to 8 volt zener voltage of the transistor 52 base-emitterjunction, essentially no gating current will flow to control gate 61 ofcontrol SCR 51 SCR 51 thus continues to block the current to heater 44.

During the negative half cycle of the AC supply voltage, SCR 25 revertsto the blocking state; the collectorbase diode action of transistor 52limits the reverse voltage on SCR 25 to approximately 0.6 volt. Therelatively large value of resistor 59 prevents the current from reachinga sufficiently high value to activate heater 44.

' When the level of accumulated ice in receptacle 13 is such that itblocks the light beam, SCR 25 is prevented from being switched to theconducting state during the positive half cycle of the AC voltage. Assoon as the voltage at terminal 63 exceeds the zener breakdown potentialof the base-emitter junction of transistor 52, current flows to thecontrol gate 61 of SCR 51, thereby gating control SCR 51 into theconduction state allowing heater 44 to be energized. Thermostatic switch36 will open to prevent further operation of motor 34 and mold heater 35thereby de-activating the ice maker.

In this application, components of the present inventionfoundsatisfactory are:

ITEM VALUE OR NO.

SCR 51 GE Cl03B Resistor 58 K ohm I meg ohm Resistor 59 33K ohm Resistor62 ll( ohm PNP transistor 52 is similar to GE 2N5354 with the exceptionthat it is not required to meet any of the conventional amplifyingspecifications. Trigger SCR used in this application is a signal levelswitching device having an anode gate, similar to GE C13, but packagedin a transparent plastic envelope to permit radiant energy to impingeupon the base junctions.

It should be noted that, because of the particular connection andinterrelation of PNP transistor 52 and trigger SCR 25 in conjunctionwith control gate 61 of control SCR 51, these components, with theexception of the anode-cathode junction of control SCR 51, are notsubjected to more than i 8 olts thus permitting the use of inexpensivenon-critical low voltage rated components.

in one embodiment of the invention, the control circuit 32 is packagedin a molded transparent polycarbonate box having integrally moldedtherein a focusing lens for increasing the sensitivity of SCR 25 to thebeam of radiant energy emitted by lamp 21. The completely packagedcircuit then is mounted on freezer compartment frame component 23 inalignment with the beam of energy traversing the receptacle 13.

It will be obvious that the specific embodiment is not limited in itsapplication to refrigerator cabinets in which the receptacle 13 issupported on the inner surface ofa freezercompartment door.

Other applications are, for example, as described in US. Pat. No.3,33l,2l5-Sh'aw, where the receptacle is mounted immediately beneath theice making apparatus and U5. Pat. No. 3,56l,231-Webb, where thereceptacle is mounted in the refrigerator fresh food compartment door.

Accordingly, while there i has been shown and described a specificembodiment of the present invention, it is to be understood that it isnot limited thereto and it is intended by the appended claims to coverall such modifications as fall within the scope thereof.

What is claimed as new and desired to secure by Leta trigger SCR and avoltage dropping resistor con-.

nected in series across said input terminals, the trigger SCR adapted tobe responsive to said external condition indication means to change itsconduction state in response to a predetermined change in said externalcondition;

a thermostatic heater current control SCR coupled across the inputterminals and having a control gate terminal;

a transistor having its base-emitter junction connected from the anodeof the trigger SCR to the control gate of the control SCR and having itsbase-collector junction connected across the anode-cathode terminals ofthe trigger SCR;

whereby, non-conduction of the trigger SCR causes a gating current toflow by zencr action of the transistor base-emitter junction to the gateterminal of the control SCR during positive half cy cles of the ACsupply and reverse current during negative half cycles of the AC supplyis provided by diode action of the transistor base-collector junction.

2. A control circuit as recited in claim 1, wherein the indication meanscomprises a beam of radiant energy and the trigger SCR is aphoto-sensitive SCR adapted to be responsive to said beam.

3. A control circuit as recited in claim I wherein the transistor is aPNP transistor.

4. A control circuit for a current activated thermostatic appliancecontrol switch comprising:

photoelectric triggering means, including a source providing a beam ofradiant energy, for supplying an indication of a predetermined externalcondition intended to initiate actuation of the thermostatic switch;

means for supplying an AC voltage including first and second inputterminals;

a photo-sensitive trigger SCR and a voltage dropping resistor connectedin series across said input terminals, the trigger SCR adapted to beresponsive to said photoelectric triggering means to change itsconduction state in response to a predetermined change in said externalcondition;

a thermostatic heater current control SCR coupled across the inputterminals and having a control gate terminal;

a PNP transistor having its emitter-base junction connected from theanode of the trigger SCR to I the control gate of .the control SCR andhaving its collector-base junction connected across the anode-cathodeterminals of the trigger SCR.

5. In combination with an automatic ice making system of the type havingan ice maker, an ice storage receptacle and electrical control meansincluding a heater and a thermostatic switch adapted to be responsive tothe heater. to control the operation of the ice maker as a function ofthe level of ice pieces in the receptacle, a control circuit foractuating the thermostatic switch comprising;

means for supplying an AC voltage including first and second inputterminals;

photoelectric triggering means supplying an indication of the level ofice pieces in the receptacle intended to initiate actuation of thethermostatic switch, said triggering means including a source, connectedacross said input terminals, providing a beam of radiant energypositioned so as to traverse the receptacle at a predetermined level;

a heater current control SCR for controlling actuation of the heater,said SCR being coupled across said input terminals and further having acontrol gate terminal;

a gating circuit for gating the heater current control SCR intoconduction when the quantity of ice pieces in the receptacle reaches apredetermined level, including a photo-sensitive trigger SCR and avoltage dropping resistor coupled in series across said input terminals,said trigger SCR adapted to be responsive to the photoelectrictriggering means so as to be switched to the non-conduction state whenthe quantity of ice pieces is above the predetermined level, and

a PNP transistor having its emitter-base junction connected from theanode of the trigger SCR to the control gate of the control SCR andhaving its collector base junction connected across the anode-cathodeterminals of the trigger SCR; whereby, when the trigger SCR is switchedto the non-conduction state, during the positive half cycle of the ACsupply, a gating current is caused to flow by zener action of thebase-emitter junction of the PNP transistor to the control gate of thecontrol SCR, causing the control SCR to be switched into the conductionstate, allowing current to flow to actuate the heater, which in turnactuates the thermostatic switch, thereby de-activating the ice maker.

1. A control circuit for a current activated thermostatic appliancecontrol switch comprising: means for supplying an indication of apredetermined external condition intended to initiate actuation of thethermostatic switch; means for supplying an AC voltage including firstand second input terminals; a trigger SCR and a voltage droppingresistor connected in series across said input terminals, the triggerSCR adapted to be responsive to said external condition indication meansto change its conduction state in response to a predetermined change insaid external condition; a thermostatic heater current control SCRcoupled across the input terminals and having a control gate terminal; atransistor having its base-emitter junction connected from the anode ofthe trigger SCR to the control gate of the control SCR and having itsbase-collector junction connected across the anode-cathode terminals ofthe trigger SCR; whereby, non-conduction of the trigger SCR causes agating current to flow by zener action of the transistor base-emitterjunction to the gate terminal of the control SCR during positive halfcycles of the AC supply and reverse current during negative half cyclesof the AC supply is provided by diode action of the transistorbase-collector junction.
 2. A control circuit as recited in claim 1,wherein the indication means comprises a beam of radiant energy and thetrigger SCR is a photo-sensitive SCR adapted to be responsive to saidbeam.
 3. A control circuit as recited in claim 1 wherein the transistoris a PNP transistor.
 4. A control circuit for a current activatedthermostatic appliance control switch comprising: photoelectrictriggering means, including a source providing a beam of radiant energy,for supplying an indication of a predetermined external conditionintended to initiate actuation of the thermostatic switch; means forsupplying an AC voltage including first and second input terminals; aphoto-sensitive trigger SCR and a voltage dropping resistor connected inseries across said input terminals, the trigger SCR adapted to beresponsive to said photoelectric triggering means to change itsconduction state in response to a predetermined change in said externalcondition; a thermostatic heater current control SCR coupled across theinput terminals and having a control gate terminal; a PNP transistorhaving its emitter-base junction connected from the anode of the triggerSCR to the control gate of the control SCR and having its collector-basejunction connected across the anode-cathode terminals of the triggerSCR.
 5. In combination with an automatic ice making system of the typehaving an ice maker, an ice storage receptacle and electrical controlmeans Including a heater and a thermostatic switch adapted to beresponsive to the heater to control the operation of the ice maker as afunction of the level of ice pieces in the receptacle, a control circuitfor actuating the thermostatic switch comprising: means for supplying anAC voltage including first and second input terminals; photoelectrictriggering means supplying an indication of the level of ice pieces inthe receptacle intended to initiate actuation of the thermostaticswitch, said triggering means including a source, connected across saidinput terminals, providing a beam of radiant energy positioned so as totraverse the receptacle at a predetermined level; a heater currentcontrol SCR for controlling actuation of the heater, said SCR beingcoupled across said input terminals and further having a control gateterminal; a gating circuit for gating the heater current control SCRinto conduction when the quantity of ice pieces in the receptaclereaches a predetermined level, including a photo-sensitive trigger SCRand a voltage dropping resistor coupled in series across said inputterminals, said trigger SCR adapted to be responsive to thephotoelectric triggering means so as to be switched to thenon-conduction state when the quantity of ice pieces is above thepredetermined level, and a PNP transistor having its emitter-basejunction connected from the anode of the trigger SCR to the control gateof the control SCR and having its collector base junction connectedacross the anode-cathode terminals of the trigger SCR; whereby, when thetrigger SCR is switched to the non-conduction state, during the positivehalf cycle of the AC supply, a gating current is caused to flow by zeneraction of the base-emitter junction of the PNP transistor to the controlgate of the control SCR, causing the control SCR to be switched into theconduction state, allowing current to flow to actuate the heater, whichin turn actuates the thermostatic switch, thereby de-activating the icemaker.